The reason for travel might differ, yet pathways of pilgrimage have a similar impact on civilizational progress along their course as do traditional trade routes. In the case of Mecca, trade and pilgrimage routes even overlap. In pre-Islamic times, the city of the Quraysh tribe is both an important center of trade and a center of pilgrimage. With the advent of Islam, pilgrimage comes to the fore. Mecca, especially during the pilgrimage month of Dhū lḤijjah, develops into a destination for tens of thousands, then hundreds of thousands, and finally millions of pilgrims from all over the Islamic world. Mecca not only becomes a place of spiritual renewal and social unity, but also a dynamic hub for new ideas and advancements. Books of all disciplines are traded here and—with Arabic as the lingua franca—also understood throughout the Islamic world.